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"Whereas the prototypical masculine body shape involves an angular
V-shape induced by a low WCR (Horvath, 1981) and moderate heaviness
(Furnham and Radley, 1989), a curved (“hourglass”) body shape
characterized by a WHR of about 0.7 and a slender build is associated
with femininity and female attractiveness (Singh and Young, 1995)."

They also cite the book Marketing Aesthetics when referring to the general concept. I'm not sure if it contains an empirical study, but it might have more evidence.

I found that previous study when I was researching the literature for my article on font psychology. You might find value in my article as well. I explain more details on the curved vs. angular relationship.